The transition piece in a gas turbine is a tubular member which connects a combustor of the combustion system of the gas turbine to the first stage of the turbine. In conventional constructions, an aft mount of the transition piece or duct is welded to and protrudes from the transition piece body upstream of the aft frame as shown in FIGS. 1 and 2 of the drawings. The aft mount on the transition piece 10 in this prior construction comprises a tubular projection 12 with two diametrically opposed support lugs (one shown at 14) provided with aligned holes for receiving a bolt 16. This bolt will extend through a sleeve portion 18 of a bracket 20 secured to the first turbine stage, indicated at 22. The projection 12 is welded to the transition piece 10 upstream of an enlarged frame portion 24 of the transition piece which is designed to engage the first stage nozzle contact 22. The aft mount welded juncture to the transition piece body 10 is at a relatively thin metal area of the body to permit high heat flux through the metal from the high temperature internal combustion gas flow. This thin, high temperature metal is very flexible and thus has minimal thermal stress and fatigue cracking. However, vibratory motion of the combustion system is sufficiently large to cause significant wear at interfaces. In addition, the mounting arrangement is expensive to manufacture.
Other prior aft mount designs consist of thin plate buttresses welded to the transition piece body and extended to the support point. These plates are in an axial-radial plane and attached at a similar location as the aft mount tubular projection described above. This particular design has been plagued with fatigue cracking.
The present invention provides a significantly stiffer aft mount for the transition piece, thereby reducing vibratory motion of the combustion system. Simultaneously, by attaching the aft mount section of integral design to the lower temperature extremity of the aft frame, and using an optimal geometric contour into the frame, thermal stress is maintained within allowable limits. The integral aft frame/mount in accordance with this invention can be cast as one piece in order to reduce parts, assembly time and welding which, in turn, reduces costs.
In the exemplary embodiment, the present invention includes a mount which is integral with the structural frame at the aft end of the transition piece. Specifically, the aft mount section is filletted into a center rib of the aft frame. At the same time, the aft mount curves 90.degree. upwardly and rearwardly, i.e., in an upstream direction, terminating in a transversely oriented attachment tube adapted to receive a mounting bolt.
In its broadest aspect, the invention relates to a transition piece for a gas turbine comprising a tubular body having a downstream end including a frame surrounding an exit opening in the tubular body, and an aft mount connector integrally formed with the frame.
In another aspect, the present invention comprises a transition piece for a gas turbine comprising a tubular body having an upstream end and a downstream end, the downstream end formed with an integral frame surrounding an opening at the downstream end; and an aft mount connector adapted to connect the transition piece to a first stage nozzle of the gas turbine, the aft mount connector formed integrally with the frame.
In summary, the present invention has two advantages. First, the rigidity of the transition piece structural support is greatly increased thereby reducing vibratory motion and interface wear. Second, the cost of the transition piece assembly is substantially reduced due to the elimination of the separate aft mount. In addition, it will be appreciated that this integral aft frame/mount can be retrofit to existing gas turbines.
Other objects and advantages of the invention will become apparent from the detailed description which follows.